Diffuser for aeration of a fluid

ABSTRACT

An elongate diffuser ( 10 ) comprises a diffuser body ( 30 ), and a membrane ( 20 ) attached so that introduction of gas at a working pressure into the diffuser displaces part of the membrane ( 20 ) from contact with the diffuser body ( 10 ) providing an elongate sealed compartment ( 50 ) between the membrane ( 20 ) and a surface ( 32 ) of the diffuser body ( 30 ). The gas can pass from the compartment ( 50 ) through the membrane ( 20 ) for aeration of fluid in which the diffuser ( 10 ) is immersed. The diffuser body surface ( 32 ) which bounds the compartment ( 50 ) is recessed away from the membrane ( 20 ) in use, to contribute to the lateral cross sectional area of the compartment ( 50 ) and facilitate distribution of gas along the diffuser by the compartment ( 50 ). An automatic purge valve for purging water from a gas feed pipe of a diffuser is also disclosed.

FIELD

The present disclosure relates to a diffuser for aeration of a fluid.The present disclosure also relates to a purge valve which may beprovided in an air feed conduit of the disclosed diffuser.

Definition

In the specification, the term “comprising” shall be understood to havea broad meaning similar to the term “including” and will be understoodto imply the inclusion of a stated integer or step or group of integersor steps but not the exclusion of any other integer or step or group ofintegers or steps. This definition also applies to variations on theterm “comprising” such as “comprise” and “comprises”.

BACKGROUND

In waste water treatment, aeration process supplies oxygen to microbeswhich consume waste material, thereby aiding its removal from the water.In carrying out this process, aeration diffusers are used to createbubbles from a submerged position in a treatment tank.

One known type of diffuser has a rigid body with an elastomeric membranefitted to an upper surface of the body. Gas (normally air) is introducedinto the diffuser, and passes through small slits in the membrane toform bubbles in the waste water. In use, this type of diffuser providesa small space or void between the upper surface of an upper wall of thebody of the diffuser and a lower surface of the membrane, this spacebeing formed by stretching of membrane by the introduction of air, underpressure, between the body and the membrane. When the membrane isstretched, the slits in the membrane open to allow escape of air to formbubbles.

It is known to supply air to a network of submerged diffusers by pipework which is attached to the floor of the tank or attached to one ormore submersible frames which provide weight to counter buoyancy forceswhich act on the diffusers due largely to the contained air.

Some diffusers are elongate, with lengths substantially greater thantheir widths. Such diffusers are sometimes called strip diffusers. Themembranes of such diffusers typically extend across most of the widthand most of the length of the diffuser body.

In a strip diffuser, it is important to supply air to the membrane alongsubstantially the entire length of the diffuser membrane, and to avoidlarge air pressure differences at different parts of the membrane.

Provision of air to the membrane is addressed in different ways indifferent diffusers. One type of diffuser is arranged to be mounted tothe crown of a pipe and to extend axially parallel to the pipe. Alignedair-feed orifices in the crown of the pipe and in the diffuser bodyallow air to pass from the pipe interior through the orifices in thecrown of the pipe, through orifices in the upper wall of the diffuserbody and to the membrane. This type of diffuser thus requires aconsiderable amount of pipe work in addition to the diffuser itself and,formation of multiple holes which must be formed and aligned, to allowair to pass to each diffuser from the pipe on which the diffuser ismounted. One such diffuser has a length of about two meters, so that adifferent diffuser must be used for each two meters of diffuser lengthrequired.

Another approach to providing air to the membrane along the length ofthe diffuser is provided by diffusers which do not require mountingalong the length of a pipe, but which instead provide an elongatechamber within the diffuser body, so that the diffuser body itself formsa conduit for distributing air along its length. This avoids the need toarrange mounting the entire diffuser atop a pipe and provision andalignment of multiple spaced orifices in the pipe and diffuser body, butrequires a diffuser body structure which provides a chamber or conduitalong its length. Diffuser bodies of this type are normally limited toabout four meters in length.

In both of the types of diffuser described above, one operational issueis that waste water may enter the conduit mixed with liquor that isstagnant and will be a potential problem, for example when removing thediffuser from the tank for maintenance. This can occur whether theconduit is provided by a pipe to which the diffuser body is mounted orby a conduit provided by the diffuser body.

Another problem which occurs in some diffusers is that the sealing ofthe membrane to the diffuser along the long sides of the diffuser isprovided by parts of the diffuser which extend above the edges of themembrane. This can result in a build-up of particulates, such as gritand the like, along the edges of the membrane which is not shed by theraised (inflated) shape the membrane when the diffuser is in use. Thishas been demonstrated to affect performance and life of the diffusers.

One known type of diffuser produced by Aquatec Maxcon Pty Ltd, anembodiment of which is described in Australian Patent No. 745191, usesan extruded base and extruded or sheet membrane which is sealed alongits long edges to the base by insertion of sealing parts into elongategrooves that extend adjacent long edges of the upper surface of thediffuser body. The sealing parts include a thickened part or bulb thatresists removal from the grooves and thereby attaches the membrane tothe body. The thickened part or bulb may be integrated into the membranedirectly or a separate component similar to lengths of spline that areused to attach an insect screen mesh to a frame. At each end of thediffuser, there are further sealing devices to prevent air escape. Theupper surface of the diffuser body is flat or convex in transverse crosssection (i.e. higher at the centre than at the edges). This diffuserdoes not include a conduit nor require mounting along the length of apipe but is generally mounted transverse to a pipe and relies upon thecontained space between the upper surface of the diffuser body and themembrane, when the membrane is stretched by applied gas pressure, toallow passage of air from the centre to the ends of the diffuser. Thistype of diffuser has proven effective in use. However, it has beendiscerned that an improved, or at least alternative diffuser, isdesirable.

The reference to prior art in this specification is not and should notbe taken as an acknowledgment or any form of suggestion that thereferenced prior art forms part of the common general knowledge inAustralia or in any other country.

SUMMARY

According to a first aspect of the present disclosure, there is providedan elongate diffuser comprising:

a diffuser base comprising a diffuser body;

a membrane attached to the diffuser body;

wherein the membrane is connected to the diffuser body so thatintroduction of gas at a working pressure into the diffuser displacespart of the membrane from contact with the diffuser body to provide anelongate sealed compartment between the membrane and a surface providedmainly or wholly by the diffuser body, the compartment having a firstlateral side interface region where the membrane contacts the diffuserbody, a laterally intermediate region where the membrane is spaced apartfrom the diffuser body and a second lateral side interface region wherethe membrane contacts the diffuser body, and wherein gas can pass fromthe compartment through the membrane for aeration of a fluid in whichthe diffuser is immersed; and

wherein the diffuser body surface which bounds the compartment comprisesa recessed portion which is recessed away from the membrane between thefirst lateral interface region and the second lateral interface region,compared to a planar surface extending between the first lateral sideinterface region and the second lateral side interface region, tothereby provide the compartment with larger transverse cross sectionalsize than would be provided by a planar surface extending from the firstlateral side interface region to the second lateral interface region.

In an embodiment, the surface is recessed across at least part of thelateral distance between the first lateral side interface region and thesecond lateral side interface region.

In an embodiment, the surface is recessed across at least most of thelateral distance between the first lateral side interface region and thesecond lateral side interface region.

In an embodiment, the surface is recessed across at least 60% of thelateral distance between the first lateral side interface region and thesecond lateral side interface region.

In an embodiment, the surface is recessed across at least 75% of thelateral distance between the first lateral side interface region and thesecond lateral side interface region.

In an embodiment, the surface has a substantially uniform curvatureacross at least most of the lateral distance between the first lateralside interface region and the second lateral side interface region.

In an embodiment, the surface has a substantially uniform curvatureacross at least 75% the lateral distance between the first lateral sideinterface region and the second lateral side interface region.

In an embodiment, the surface has a substantially uniform curvatureacross at least 85% of the lateral distance between the first lateralside interface region and the second lateral side interface region.

In an embodiment, when the diffuser is inactive with substantially nogas pressure applied thereto, the membrane engages the surface of thediffuser body across the recessed region.

In an embodiment, the surface has a substantially concave form intransverse cross section.

In an embodiment, the diffuser provides a gas inlet for introducing gasinto the compartment.

In an embodiment, the diffuser provides only a single gas inlet into thecompartment.

In an embodiment, the diffuser body does not provide any gas conduit fordistributing gas along the length of the diffuser other than thecompartment.

In an embodiment, the compartment formed between the diffuser body andthe membrane provides the sole or at least primary distribution channelfor distributing gas along the length direction of the diffuser.

In an embodiment, the compartment formed between the diffuser body andthe membrane provides the only distribution channel for distributing gasalong the length direction of the diffuser.

In an embodiment, a gas inlet is provided at a first end region of thediffuser, and the compartment formed between the diffuser body and themembrane provides the primary means of distributing gas from the firstend region of the diffuser to the other, second, end region of thediffuser.

In an embodiment, the surface provides no more than one or two inletsfor introduction of gas into the compartment.

In an embodiment, a gas inlet is provided at an axially central regionof the diffuser body, and the interior compartment distributes gasbetween the inlet and the axial ends of the interior compartment.

In an embodiment, when the diffuser is oriented so that the first andsecond lateral side interface regions are horizontally spaced apart, alaterally central region of the surface is the lowest part of thesurface.

In an embodiment, the diffuser provides a gas inlet at a first axial endregion thereof, and a gas outlet at a second axial end region thereof,so that the interior compartment can be used for distributing gas from agas supply to another diffuser.

In an embodiment, the diffuser has a length of at least 1 metre.

In an embodiment, the diffuser has a length of at least 5 metres, atleast 6 metres, at least 7, at least 8, at least 9, at least 10, or atleast 11 metres.

In an embodiment, the diffuser has a length of at least 12 metres.

In an embodiment the diffuser has a length of at between 5 and 7 metres

In an embodiment, the diffuser has a width of between about 8 cm andabout 50 cm.

In an embodiment, the diffuser has a width of between about 8 cm andabout 30 cm.

In an embodiment, the diffuser has a width of between about 10 cm andabout 20 cm.

In an embodiment, the diffuser has a length to width ratio of at leastabout 12.

In an embodiment, the diffuser has a length to width ratio of at leastabout 20.

In an embodiment, the diffuser has a length to width ratio of at leastabout 30.

In embodiment the, diffuser has a length to width ratio of at leastabout 50.

In an embodiment, the diffuser has a length to width ratio of at leastabout 70.

When substantially no gas pressure is provided to the diffuser, themembrane may be in a relaxed or collapsed state. In this state,substantially the entire lateral width of the membrane may rest upon thebase surface, so that the compartment does not exist.

When a first, lower, level of gas pressure is provided to the diffuser,the membrane may be inflated, but not stretched to provide saidcompartment, which in this state has a first, smaller, cross-sectionalsize. That is, the Inflation of the membrane provides said compartment,including said laterally intermediate region of the compartment, wherethe membrane is spaced apart from the diffuser body.

When a second, higher, level of gas pressure is provided to thediffuser, the membrane may be inflated, and also stretched, to increasethe spacing between the membrane and the diffuser body at the laterallyintermediate region of the compartment, so that in this state thecompartment has a second, greater cross-sectional size.

In an embodiment, at least one axial end region the membrane is sealedagainst a surface of the diffuser base.

In an embodiment, at least one axial end region the membrane is sealedagainst a surface of the diffuser base such that a transverselyextending region of the membrane is retained in a substantially convexcross sectional shape.

In an embodiment, at least one axial end region the membrane is sealedagainst a surface of the diffuser base such that a transverselyextending region of the membrane is retained in a substantially convexcross sectional shape irrespective of whether the membrane is inflated.

In an embodiment, at least one axial end region the membrane is sealedagainst a surface of the diffuser base such that a transverselyextending region of the membrane is retained in a substantially convexcross sectional shape which corresponds substantially to the crosssectional shape of a corresponding lateral region of the membrane, at anaxially central region of the diffuser, when the membrane is inflated.

In an embodiment, at least one axial end region the membrane is sealedagainst a surface of the diffuser base such that a transverselyextending region of the membrane is retained in a substantially convexcross sectional shape which corresponds substantially to the crosssectional shape of a corresponding lateral region of the membrane, at anaxially central region of the diffuser, when the membrane is inflatedbut not stretched.

In an embodiment, at least one axial end region of the interiorcompartment is at least partially defined by a base surface end portionwhich is shaped to provide a smooth transition from a transverse crosssectional shape that is substantially convex closer to the correspondingend of the diffuser to a transverse cross sectional shape that isrecessed closer to an axial centre of the diffuser.

In an embodiment, the base surface end portion is shaped to allow themembrane, when substantially no gas pressure is provided and themembrane is resting upon the base surface, to smoothly transition from asubstantially convex cross sectional shape closer to the end of thediffuser, to a recessed cross sectional shape closer to an axial centreof the diffuser.

In an embodiment, the substantially convex cross sectional shape of thebase surface end portion corresponds to the cross sectional shape of themembrane at an axially central region of the diffuser, when the membraneis inflated.

In an embodiment, the substantially convex cross sectional shape of thebase surface end portion corresponds to the cross sectional shape of themembrane at an axially central region of the diffuser, when the membraneis inflated but not stretched.

In an embodiment, the recessed cross sectional shape of the base surfacealong at least a substantial part of its axial length, correspondsgenerally to a mirror image of the cross sectional shape of the membraneat an axially central region of the diffuser, when the membrane isinflated but not stretched.

In an embodiment, at least one base surface end portion is provided byan end piece component manufactured separately to the diffuser body, andthe diffuser base comprises said diffuser body and said at least one endpiece component.

In an embodiment, at least one end piece component provides a blockingregion which at least partially blocks a recess provided by the recessedportion of the diffuser body, at an end region of the diffuser.

In an embodiment, at least one base surface end portion is provided by ashaped surface of the diffuser body.

In an embodiment, the diffuser comprises a gas inlet for passage of gasinto the compartment.

In an embodiment, at least one base surface end portion provides saidgas inlet.

In an embodiment, at least one end piece component provides said gasinlet.

In an embodiment, the diffuser comprises a non-return valve associatedwith the gas inlet.

The non-return valve may be adapted to prevent or mitigate flow ofliquid which enters the cavity into the gas inlet.

In an embodiment, the diffuser comprises a fail-closed valve associatedwith the gas inlet.

In an embodiment, the diffuser body is substantial uniform in crosssection.

In an embodiment, the diffuser body is pultruded or extruded.

In an embodiment, the diffuser body is manufactured wholly or primarilyfrom plastic, fibre reinforced or glass reinforced plastic, or metal.

In an embodiment, the diffuser body underside provides a single openchannel structure.

In an embodiment, the diffuser body underside is substantially free fromadditional lateral supports or webs.

In an embodiment, the diffuser is a fine bubble diffuser.

In an embodiment, the diffuser is provided with a mounting plate formounting the diffuser to a support.

In an embodiment, the mounting plate comprises two mounting plate partswhich can be connected to provide the mounting plate.

In an embodiment, each of the two mounting plate parts can, whenseparated from the other, be operatively engaged with the diffuser bodyat substantially any desired axial position along the length of thediffuser body but when connected together can only be disengaged fromthe diffuser body at predefined axial positions.

In an embodiment, the predefined axial positions are the ends of thediffuser.

In an embodiment, each mounting plate part provides an engagementformation for engaging a first side part of the diffuser.

In an embodiment, each mounting plate part provides a transverselyextending portion which extends in use from the side of the diffuserengaged by the mounting plate part towards the other lateral side of thediffuser.

In an embodiment, each transversely extending portion is dimensioned toextend more than half the distance between the engaged side portions ofthe diffuser, but less than the full distance between the engaged sideportions of the diffuser.

In an embodiment, when the mounting plate parts are not connected,neither extends across the full distance between the engaged sideportions of the diffuser, but when they are connected the combinedtwo-part mounting plate extends between the engaged side portions of thediffuser and can thereby be retained in a fixed position relative to thediffuser.

In an embodiment, each mounting plate part provides a connectionformation for connecting with a connection formation of the othermounting plate part.

In an embodiment, the engagement formation restricts movement of themounting plate part relative to the diffuser in the transverse directionof the diffuser and allows sliding of the mounting plate part in theaxial direction of the diffuser.

In an embodiment, the two mounting plate parts are substantiallyidentical.

According to a second aspect of the present disclosure, there isprovided an elongate diffuser comprising:

a diffuser base comprising a diffuser body;

a membrane attached to the diffuser body;

wherein the membrane is connected to the diffuser body so thatintroduction of gas at a working pressure into the diffuser displacespart of the membrane from contact with the diffuser body to provide anelongate sealed compartment between the membrane and a surface providedmainly or wholly by the diffuser body, and wherein gas can pass from thecompartment through the membrane for aeration of a fluid in which thediffuser is immersed; and

wherein the diffuser body surface which bounds the compartment comprisesa recessed portion which is recessed away from the membrane in use, andwhich contributes to the lateral cross sectional area of thecompartment, to thereby facilitate distribution of gas along at least asubstantial part of the length of the diffuser by the compartment.

In an embodiment, the compartment has a first lateral side interfaceregion where the membrane contacts the diffuser body, a laterallyintermediate region where the membrane is spaced apart from the diffuserbody and a second lateral side interface region where the membranecontacts the diffuser body.

In an embodiment, the shape of the diffuser body surface provides thecompartment with larger transverse cross sectional size than would beprovided by a planar diffuser body surface extending between the firstlateral side interface region and the second lateral side interfaceregion.

According to a third aspect of the present disclosure, there is providedan elongate diffuser comprising:

a diffuser base comprising a diffuser body;

a membrane attached to the diffuser body;

wherein the membrane is connected to the diffuser body so thatintroduction of gas at a working pressure into the diffuser displacespart of the membrane from contact with the diffuser body to provide anelongate sealed compartment between the membrane and a surface providedmainly or wholly by the diffuser body; and

wherein the diffuser body and membrane are dimensioned and configured sothat said compartment can be formed without substantial stretching ofthe membrane.

According to a fourth aspect of the present disclosure, there isprovided a method of operating a diffuser to aerate a liquid comprising:

providing a diffuser in a body of liquid, the diffuser comprising adiffuser base and a membrane, wherein the membrane fits substantiallyunstressed on the base when no air gas pressure is provided to thediffuser;

operating the diffuser with a first lower level of gas pressure appliedto flex the membrane and displace at least some of the membrane awayfrom the base, to thereby form an interior compartment between themembrane and the base which acts as a conduit to distribute gas over asubstantial part of the length of the diffuser, without substantiallystretching the membrane; and

after formation of the interior compartment along substantially theworking length of the diffuser, operating the diffuser with a second,greater, level of gas pressure, sufficient to stretch the membrane, tothereby open slits or apertures therein for formation of bubbles in thebody of liquid.

In an embodiment, the method comprises use of a diffuser in accordancewith the first aspect.

In an embodiment, the method comprises use of a diffuser in accordancewith the second aspect.

In an embodiment, the method comprises use of a diffuser in accordancewith the third aspect.

In an embodiment, operating the diffuser with a first lower level of gaspressure applied comprises operating the diffuser with at a gas pressureof marginally greater than the fluid pressure immediately adjacent thediffuser.

In an embodiment, operating the diffuser with a second, greater, levelof gas pressure applied comprises operating the diffuser with at a gaspressure of at least 2 kPa greater than the fluid pressure immediatelyadjacent the diffuser.

In an embodiment, operating the diffuser with a second, greater, levelof gas pressure applied comprises operating the diffuser with at a gaspressure of between 2 and 10 kPa greater than the fluid pressureimmediately adjacent the diffuser.

According to a fifth aspect of the present disclosure, there is provideda purge valve system for use in an air inlet pipe of an air diffuser,comprising:

a purge control element movable between a first control position forclosing a water outlet when there is little or no accumulated water tobe purged, and a second control position for opening the outlet inresponse to the presence of water to be purged; and

a flow check valve through which water is, in use, purged, said flowcheck valve being a one-way valve which allows flow of watertherethrough in the purging direction and in use substantially preventsflow of water therethrough in the reverse direction.

In an embodiment the flow check valve is provided downstream, in a waterpurge flow direction, of the water outlet.

In an embodiment the purge control element comprises a float.

In an embodiment the first control position corresponds to anon-floating position of the float.

In an embodiment the water outlet comprises a seat engageable by thefloat.

In an embodiment the water outlet comprises an inlet part of the flowcheck valve.

In an embodiment the second control position corresponds to a floatingposition of the float.

In an embodiment the flow check valve comprises a flexible part which isdeformable by positive net fluid pressure on an upstream side thereof,in a water purge flow direction, into an open configuration.

In an embodiment the flexible part of the flow check valve is configuredto remain in a substantially closed configuration in the circumstancesof positive net fluid pressure on a downstream side thereof, in a waterpurge flow direction.

In an embodiment the flexible part of the flow check valve comprises anelastomer material.

In an embodiment the elastomer material is a type of rubber.

In an embodiment the flow check valve is configured to provide a slotwhich is closed in the absence of net pressure from either side of theflow check valve.

In an embodiment the flow check valve is configured so that the slotremains closed in the presence of a positive net pressure applied to adownstream side thereof, in a water purge flow direction.

In an embodiment the flow check valve is configured to provide a slotwhich is configured to be forced open by a positive net pressure appliedto an upstream side thereof, in a water purge flow direction.

In an embodiment the slot is provided by two opposed parts of the flowcheck valve.

In an embodiment the flow check valve comprises a duck-bill valve.

In an embodiment, the purge valve system comprises a float restrainingmember positionable in a first, float restraining, position to retainthe float substantially in the first, non-floating, position.

In an embodiment the float restraining member is moveable by providingincreased air pressure in a vessel from which water is to be purged.

In an embodiment the float restraining member is moveable by providingincreased air pressure in the air inlet pipe from which water is to bepurged.

Any one or more features and/or characteristics described in relation tothe first aspect may be incorporated mutatis mutandis in the diffuser ofthe second aspect, the diffuser of the third aspect and/or into themethod of the fourth aspect.

Any one or more features and/or characteristics described in relation tothe fifth aspect may be incorporated mutatis mutandis in the diffuser ofthe first aspect, the diffuser of the second aspect, the diffuser of thethird aspect and/or into the method of the fourth aspect.

According to a sixth aspect of the present disclosure, there is providedan air shut off valve for use in an air inlet pipe of an air diffuser,the air shut off valve being adapted to shut off air flow to thediffuser in event of failure of an air diffusion membrane, the air shutoff valve comprising: a valve member adapted to remain in an open,inoperative, position when air flow to the diffuser is below a thresholdlevel, to move into a closed, shut-off, position in response to the airflow exceeding the threshold level and, after movement into the closedposition, to remain in the closed position despite the air flow leveldropping to below the threshold level.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will be described below, in detail, with reference toaccompanying drawings. The primary purpose of this detailed descriptionis to instruct persons having an interest in the subject matter of theinvention how to carry the invention into practical effect. However, itis to be clearly understood that the specific nature of this detaileddescription should not be considered to supersede the generality of thepreceding Summary section or appended claims. In the accompanyingdiagrammatic drawings:

FIG. 1(a) is a perspective view of a base part of a diffuser foraeration of a fluid in accordance with an embodiment of the presentdisclosure;

FIG. 1(b) is a cross sectional view of the diffuser base part of FIG.1(a) diffuser;

FIG. 2 is a is a cross sectional view of an elastomeric membrane for usewith the base shown in FIG. 1 ;

FIG. 3 is a schematic cross sectional view illustrating theconfiguration of a diffuser comprising the base part of FIG. 1 and theelastomeric membrane of FIG. 2 when no air is being supplied to thediffuser;

FIG. 4 is a schematic cross sectional view illustrating theconfiguration of the diffuser of FIG. 3 when sufficient air is providedto raise part of the elastomeric membrane but not to substantiallystretch it;

FIG. 5 is a schematic cross sectional view illustrating theconfiguration of the diffuser of FIG. 3 when sufficient air is providedto stretch the elastomeric membrane and operate the diffuser;

FIG. 6 is a schematic perspective view of an embodiment of a diffuser,consistent with FIGS. 1 to 5 , when no air is being supplied to thediffuser;

FIG. 7 is a schematic perspective view of the diffuser of FIG. 6 whensufficient air is provided to stretch the elastomeric membrane andoperate the diffuser;

FIG. 8 is a schematic perspective view of the diffuser of FIGS. 6 and 7with the elastomeric membrane omitted to show internal structure;

FIG. 9(a) is a schematic perspective view of the diffuser of FIGS. 6 to8 ;

FIG. 9(b) is a schematic perspective view of the diffuser of FIGS. 6 to8 , with the elastomeric membrane fully inflated and partially cut awayto show internal structure;

FIG. 9(c) is a schematic perspective view of the diffuser of FIGS. 6 to8 with the elastomeric membrane relaxed (fully deflated) and partiallycut away to show internal structure;

FIG. 9(d) is a schematic perspective view of an elastomeric membranetailored for use with the diffuser of FIGS. 6 to 9 (c);

FIG. 9(e) is a partially cut away schematic perspective view of theelastomeric membrane in isolation but showing an example shape of an endregion thereof when fitted to a diffuser as shown in FIGS. 6 to 9 (c);

FIG. 10(a) is schematic perspective view of a tapered end inletcomponent as shown in FIGS. 8, 9 (b) and 9 c;

FIG. 10(b) is an exploded view of the tapered end inlet component ofFIG. 10(a);

FIG. 10(c) is a perspective view of an end region of a diffuser basebody with a cut-out for accommodating a tapered end inlet component asshown in FIGS. 10(a) and 10 (b),

FIG. 11(a) is schematic perspective view of an alternative embodiment ofa tapered end inlet component slightly different in shape to the taperedend inlet component FIG. 10(a);

FIG. 11(b) is an exploded view of the tapered end inlet component ofFIG. 11(a);

FIG. 12 is a schematic perspective view of a tapered end component whichdoes not include an air inlet;

FIG. 13(a) is schematic perspective view of an air inlet component foruse in an axially central region of a diffuser;

FIG. 13(b) is an exploded view of the air inlet component of FIG. 13(a);

FIGS. 14(a) and 14(b) are schematic perspective views of an end retainercomponent;

FIG. 15(a) is an enlarged view of FIG. 9(d);

FIG. 15(b) is an enlarged view of FIG. 9(e);

FIG. 16 is a schematic perspective view illustrating assembly of adiffuser by attachment of an elastomeric membrane onto a base part of adiffuser;

FIG. 17 is a schematic perspective view of two baseplate parts of afixing arrangement for fixing the diffuser to a floor;

FIG. 18 is a schematic perspective view of the two baseplate parts ofFIG. 17 connected together;

FIG. 19 is a schematic end view illustrating connection of each of thetwo baseplate parts of FIGS. 17 and 18 , separately, to a diffuser body;

FIGS. 20(a), 20(b) and 20(c) illustrates an alternative embodiment of adiffuser, in which the air inlet is provided in an axially centralregion, utilising the air inlet component of FIGS. 13(a) and 13(b);

FIG. 21 is a schematic cross sectional view of an alternative embodimentof a base part of a diffuser and associated membrane, in an in-useconfiguration;

FIG. 22 is a schematic cross sectional view of a further alternativeembodiment of a base part of a diffuser and associated membrane, in anin-use configuration;

FIG. 23 is schematic perspective exploded view of an alternativeembodiment of a tapered end inlet component, with similarities to thetapered end inlet components of FIGS. 10(a), 10(b), 11(a) and 11(b),which includes a purge valve for purging water accumulated in an inletpipe;

FIG. 24 is a schematic exploded end view of the tapered end inletcomponent of FIG. 23 , showing some internal detail in broken lines;

FIG. 25 is a schematic side view of the tapered end inlet component ofFIG. 23 , assembled, and in a passive, non-air flow configuration,showing some internal detail in broken lines;

FIG. 26 is a schematic end view of the tapered end inlet component asshown in FIG. 25 , showing some internal detail in broken lines;

FIG. 27 is a schematic longitudinal cross sectional view of the taperedend inlet component as shown in FIG. 25 ;

FIG. 28 is a schematic transverse cross sectional view of the taperedend inlet component as shown in FIG. 25 ;

FIG. 29 is a schematic side view of the tapered end inlet component ofFIG. 23 , assembled, and in an active, air flow configuration, showingsome internal detail in broken lines;

FIG. 30 is a schematic longitudinal cross sectional view of the taperedend inlet component as shown in FIG. 29 ;

FIG. 31 is a schematic transverse cross sectional view of the taperedend inlet component as shown in FIG. 29 ;

FIG. 32 is schematic perspective exploded view of an alternativeembodiment of a tapered end inlet component, with similarities to thetapered end inlet component of FIG. 23 , but with an alternativeembodiment of a purge valve;

FIG. 33 is a schematic exploded end view of the tapered end inletcomponent of FIG. 32 , showing some internal detail in broken lines;

FIG. 34 is a schematic side view of the tapered end inlet component ofFIG. 32 , assembled, and in a passive, non-air flow configuration,showing some internal detail in broken lines;

FIG. 35 is a schematic longitudinal cross sectional view of the taperedend inlet component as shown in FIG. 34 ; and

FIG. 36 is a schematic transverse cross sectional view of the taperedend inlet component as shown in FIG. 34 .

DETAILED DESCRIPTION OF THE EMBODIMENTS

With reference to the accompanying drawings, embodiments of diffusersfor aeration of a fluid will now be described.

With reference to FIGS. 1 to 5 , an embodiment of a diffuser inaccordance with the present disclosure, generally designated 10,comprises a flexible member 20 which may be an elastomeric membrane, anda diffuser base body 30.

As illustrated in FIGS. 1(a) and 1(b) (referred to collectively as FIG.1 ), the diffuser base body 30 in this embodiment comprises a mainsurface 32, which is, in normal use, upwardly facing. The main surface32 is provided on an in-use upper wall 34 of the diffuser base body 30.The main surface 32 is recessed in an in-use downwards direction. Inthis embodiment, at least part of the main surface 32 is curved so thatat least some of the main surface is lower than it would be if the mainsurface were planar. In this embodiment at least part of the mainsurface the 32 is part cylindrical, although it should be appreciatedthat other geometries of curvature could be used. Similarly, in thisembodiment, at least part of the in-use upper wall 34 is partcylindrical. The diffuser base body 30 may be pultruded or extrudedusing plastic, fibre reinforced or glass reinforced plastic or metalsuch as aluminium. It could also be roll formed from metal material suchas stainless steel or even 3D printed. The break lines in FIG. 1(a) areintended to indicate that the base can be cut, or otherwise manufacturedto substantially any manageable length.

The diffuser base body 30 further comprises first and second side walls36, 38 on which the upper wall 34 is supported in use. In thisembodiment, the first and second side walls 36, 38 are substantiallyparallel and are laterally spaced apart by the upper wall 34.

Depending from a bottom region of each of the first and second sidewalls 36, 38 is a respective inwardly directed flange wall 40, 42.

The diffuser base body 30 further comprises first and second attachmentregions 44, 46 for attachment of the flexible member 20 to the diffuserbase body 30. In this embodiment, the attachment regions 44, 46 areprovided substantially where the upper wall 34 meets the first andsecond side walls 36, 38 but it will be appreciated that in otherembodiments, they could be provided wholly on the upper wall 34 orwholly on the first and second side walls 36, 38.

Each of the first and second attachment regions 44, 46 defines acorresponding groove 45, 47 for receiving a sealing strip 25, 26 of theflexible member 20 illustrated in FIG. 2 (which will be describedfurther below).

The diffuser base body 30 may be regarded as being of generallyrectangular cross section defining an interior channel 48, which is openat the bottom of the diffuser base body 30, as the laterally inward endsof the inwardly directed flange walls 40, 42 are spaced apart. However,the main surface 32, and in this embodiment the in-use upper wall 34, isrecessed towards the centre of the channel 48. Further, the first andsecond attachment regions 44, 46 depart from a rectangular shape. Ofcourse, alternative embodiments may be differently shaped withoutdeparting from the scope of the present disclosure.

As illustrated in FIG. 2 , the flexible member 20 comprises a sheet offlexible material 21 dimensioned to fit upon the diffuser base body 30.The flexible member 20 has a generally laterally central region 22 andfirst and second lateral side regions 23, 24. Provided at or adjacentthe side regions 23, 24 are respective first and second sealing strips25, 26, which extend along the side regions 23, 24 in the lengthdirection of the flexible member 20. In this embodiment, the sealingstrips 25, 26 are in the form of deformable projections which, in thisembodiment, widen as they project further from the sheet of flexiblematerial 21 to facilitate retention in the groove 45, 47 and may beregarded as bulbous in form. In this embodiment, a wider part of eachsealing strip 25, 26 has an internal void or passageway 27, 28 whichextends along the sealing strip. The internal passageways may assistdeformation of the sealing strips, and thus insertion into the grooves45, 47, but are not necessary in all embodiments.

The flexible member 20 may be regarded as having an in-use internal face29A and an in-use external face 29B, with the sealing strips 25, 26projecting from the internal face 29A.

The flexible member 20 may be formed by extrusion, with the sealingstrips 25, 26 integrally formed therein. Other embodiments may providesealing strips formed separately to membrane, for example, providing asheet membrane and separate sealing strips which may be forced intogrooves of the diffuser body in order to retain lateral edges of thesheet in the grooves, for example, in a manner corresponding to the waysplines are used to retain edge regions of sheets of fly screen materialframes provided for use in door or window openings.

FIG. 3 illustrates, in transverse cross section, the diffuser 10assembled for use, and with the flexible member 20 overlaid on the mainsurface 32 of the diffuser base body 30. The sealing strips 25, 26 areretained in the grooves 45, 47.

It will be understood that wider parts of the sealing strips 25, 26 aredeformable such that they compress when forced through the relativelynarrow openings of grooves 45, 47 and then expand to press against theinner surface of the grooves, to thereby provide a sealed connection ofthe flexible member 20 to the diffuser base body 30. Moreover, sealingstrips 5 and grooves 4 are dimensioned such that the sealing strips areheld within the grooves once the flexible member 20 has been fitted tothe diffuser base body 30. The retention and/or sealing of the sealingstrips 25, 26 in the grooves 45, 47 may, if desired, be enhanced byinserting one or more substantially incompressible members (such assolid rod or wire), or by application of a fluid which subsequentlycures to become substantially solid, into the internal voids orpassageways 27, 28 or by application of a of sealant material suitableto adhere to both the flexible member 20 to the diffuser base body 30.

This connection of the flexible member 20 to the diffuser base body 30provides an effective seal along the lateral sides of the diffuser 10.It should be appreciated that the diffuser 10 may be many metres long,as will be described in more detail in due course. (It will beappreciated that there is a need to provide a seal between the flexiblemember 20 and the diffuser base body 30 at the ends, as well as alongthe lateral sides, and also to provide ingress of air into the diffuser,and these aspects will be described in due course.)

The configuration illustrated in FIG. 3 corresponds to a condition inwhich there is substantially no gas pressure applied to the diffuser 10.Substantially the entire width of the flexible member 20 is in contactwith the main surface 32 of the diffuser base body 30. The flexiblemember 20 is relaxed and not stretched. The flexible member 20 isprovided with small slits or other apertures to allow air to pass fromthe interior side 29A to the exterior side 29B, to allow bubbleformation. In the relaxed and unstretched condition of the flexiblemember 20, these apertures are substantially closed. Thus, in thiscondition, the flexible member 20 lies smoothly along the main surface32 of the diffuser base body 30 without open slits or apertures, so thatit effectively prevents ingress of waste water (or other liquid in whichthe diffuser 10 is immersed) to prevent ingress of liquid into thediffuser or into associated pipework via the diffuser. To achieve this,It is important to have the flexible member 20 accurately dimensionedfor the diffuser: if the flexible member 20 is too loose the excessmaterial will likely cause it to crease and split, and if the flexiblemember 20 is too taut, the slits will open without application of air tostretch it, likely allowing unintended and undesirable ingress ofliquid. To help ensure an appropriate dimensional fit throughout thelife of the flexible member 20, it is important to provide a flexiblemember 20 which will provide minimal creep during its operational life.

FIG. 4 illustrates, in transverse cross section, the assembled diffuser10, and the configuration illustrated in FIG. 4 corresponds to acondition in which there is sufficient gas pressure applied to thediffuser 10 to cause the flexible member 20 to flex and to inflate, butnot to substantially stretch. The inflation of the flexible member 20creates a gas-filled interior compartment 50 between the flexible member20 and the main surface 32 of the diffuser base body 30, whicheffectively forms a pipe or conduit which can distribute air along thelength of the diffuser 10. This pipe or conduit is formed withoutstretching or stressing of the flexible member 20 or opening of theapertures or slits therein. The cross sectional size of the interiorcompartment 50, and thus the capacity of the pipe or conduit which itforms, can then be increased by increasing the applied gas pressure, aswill be described below. The action of inflating the flexible member 20to a convex profile as shown in FIG. 4 promotes the removal of anydebris which may settle on the membrane during non-operating time suchas in an intermittent aeration application (e.g. in Sequential BatchReactors (SBR) or Intermittently Decanted Extended Aeration (IDEA)).

FIG. 5 illustrates, in transverse cross section, the assembled diffuser10, with a configuration corresponding to a working condition, in whichthere is sufficient gas pressure applied to the diffuser 10 to cause theflexible member 20 to stretch, so that the perforations or slits openand air can pass therethrough and form bubbles in the liquid in whichthe diffuser 10 is immersed.

The increased applied gas pressure, compared to the condition of FIG. 4, causes stretching of the flexible member 20, which increases the crosssectional size of the size of the interior compartment 50, and thus thecapacity of the pipe or conduit which it forms.

It will be appreciated that the pipe or conduit or conduit formed by theinterior compartment 50 is relied upon for distribution of gas/air alongthe length of the diffuser 10. No other pipe or conduit structure isprovided by the diffuser 10 between its ends, and no other pipe reliedupon for distributing gas between the ends of the diffuser.

It will further be appreciated that the recessed shape of the mainsurface 32 plays an important role.

The interior compartment 50 is provided by the inflated (and/or)stretched flexible member 20, and the main surface 32. At either lateralside of the compartment 50, the compartment is bounded by a lateral sidewhich may be regarded as the most inward point of contact between theflexible member 20, and the main surface 32. These lateral sides aredesignated S1 and S2 in FIG. 5 . By way of illustration of the recessednature of the main surface 32, a straight line between S1 and S2 isincluded in FIG. 5 , shown as a dashed line 52. From comparison of thedashed line 52 and the main surface 32, it can be seen that the recessedshape of the main surface 32 substantially increases the cross sectionalsize of the interior compartment, compared to use of a straight orplanar surface extending between the lateral sides S1, S2 of theinterior compartment 50.

Further, the initial formation of an interior compartment 50 whicheffectively forms a pipe or conduit, without stretching of the flexiblemember 20, by applying a relatively low air pressure, and thenincremental increase in gas pressure to stretch the flexible member 20to increase the size of the pipe or conduit which it provides, helpavoid deformation or creasing of the flexible member 20 which mightdamage it, and thereby assist in providing a flexible member 20 with along working life. In the described embodiment, features of the diffuser10 at or adjacent the ends of the diffuser, which will be describedhereafter, also contribute to avoiding application of undue stresses tothe flexible member 20.

The flexible member inflates (without substantial stretching) at anypressure greater than the surrounding fluid pressure (but insufficientto substantially stretch the flexible member).

The flexible member stretches, and the diffuser diffuses air, atpressures ranging from approximately 2 kPa to approximately 15 kPa abovethe surrounding fluid pressure, depending on the air flux and conditionof the diffuser, for example, as a result of fouling from precipitatesand biological films.

The formation of the compartment between the unstretched flexible memberand the base enables air to be distributed over considerable axiallengths of diffuser before the flexible member is required to stretch.This effectively provides an axially extending conduit, formed betweenthe flexible member and the base, so that it is not necessary to providea separately formed conduit (such as an enclosed conduit formed in orbelow the base) for distributing the gas along substantial lengths ofdiffuser.

By way of comparison with diffusers of the type disclosed in AustralianPatent No. 745191 (to Aquatec Maxcon), in which stretching of theflexible member (membrane) is required to provide a compartment betweenthe flexible member and the base so that the compartment can act as aconduit, attempts to distribute gas along lengths similar to thoseachievable by diffusers in accordance with the present disclosureresulted in the membrane becoming unstable and fluttering (oscillatingrapidly and erratically) causing the air distribution to be poor and themembrane to fatigue rapidly.

In a particular embodiment of the diffuser base body 30, the width ofthe diffuser base body 30 is about 15.5 cm. A radius of curvature of therecessed surface 32 (which in this embodiment is part-cylindrical) isabout twice the width of the diffuser base body 30. The wall thicknessesare mostly about 3-4 mm (although wall thicknesses are greater in someareas, such as adjacent the grooves 46, 47). Of course, alternativedimensions and shapes could be used, including much thinner material, aslittle as 1 mm in thickness.

FIGS. 6 to 9 (c) illustrate a practical embodiment of a diffuser inaccordance with the present disclosure. As the embodiment of FIGS. 6 to9 (c) is consistent with the schematic cross sectional views of FIGS. 3to 5 , corresponding reference numerals are used. It will be understoodthat the schematic cross sectional views of FIGS. 3 to 5 do not showcomponents of the diffuser 10 other than the flexible member 20 and thediffuser base body 30, but that FIGS. 6 to 9 (c) do include additionalcomponents.

It should be appreciated that although illustrated as being fairlyaxially short for ease of illustration, the illustrated diffuser 10 maybe very large in axial length compared to its lateral width. By way ofexample, in one successfully tested embodiment, the width of thediffuser 10 is approximately 15.5 cm, and the length approximately 12metres, so that the length is approximately 75 times the width.Practical embodiments may be limited to about 6 metres in length forease of transportation, although greater lengths, probably up to about12 metres may be practicable under some circumstances.

FIG. 6 illustrates in schematic perspective view, the diffuser 10 in acondition in which there is no air flow. The flexible member 20 is incontact with the recessed main surface 32 along most of the length ofthe diffuser 10, corresponding to the configuration illustrated in FIG.3 . However, it should be noted that at the ends 60, 61 of the diffuser10, the end regions of the flexible member 20 are retained and sealed byretaining clamps 1400 in a cross sectional shape substantiallycorresponding to the inflated but not stretched shape of the flexiblemember 20 illustrated in FIG. 4 , that is, with laterally central region22 of the flexible member 20 extending outwardly (which in thisembodiment corresponds to an upwards direction) beyond the side regions23, 24. Further, the flexible member 20 transitions between the end(convex) and axially central (concave) shapes smoothly and fairlygradually. In an embodiment, this gradual transition is facilitated byshaped end pieces (1000, 1200, but not shown in FIG. 6 ) which will bedescribed in due course. The gradual transition in shape of thesupported flexible member is provided by a surface (which will bedescribed in more detail in due course) onto which the flexible member20 can collapse, in the absence of gas pressure, without causingwrinkles or other stress inducing features.

It will also be noted that the diffuser is provided with an air inlet1250 and with a plurality of mounting plate arrangements 1700 tofacilitate mounting to a bottom of a pool, a frame, or to some otherobject or structure as desired.

FIG. 7 illustrates in schematic perspective view, the diffuser 10 in acondition in which there is full working air flow. The flexible member20 is inflated and stretched, so that the axially central region issubstantially in the cross sectional configuration illustrated in FIG. 5. However, discussed above in relation to FIG. 6 , the end regions ofthe flexible member 20 are retained in configuration substantiallycorresponding to the inflated but not stretched shape illustrated inFIG. 4 . Thus again, there is a transition between the end regions (heldin the inflated but not stretched shape) and the central region alongmost of the length of the diffuser 10, corresponding to the inflated andstretched configuration illustrated in FIG. 5 . This transition isfairly gentle, as it is a transition between the inflated andunstretched shape and the inflated and stretched shape. It should beappreciated that a transition region of similar axial length, butproviding a transition between the uninflated shape (of FIG. 3 ) and afully inflated and stretched shape would likely be substantially lessgentle and inflict substantially greater stress on the transition regionof the flexible member 20.

FIG. 8 illustrates in schematic perspective view, the diffuser 10, asshown in FIGS. 6 and 7 , but with the flexible member 20 omitted so thatinterior detail of the diffuser 10 can be seen. The internal featuresshown in FIG. 8 can also be seen in FIGS. 9(b) and 9(c) which show theflexible member 20 partially cut away rather than omitted. Further, FIG.9(a) illustrates that an air inlet is provided at one end 61 of thediffuser 10, while the other end 62 is blanked off.

For most of the length of the diffuser 10, the surface which in usefaces the interior surface 29A of the flexible member 20 comprises themain surface 32, which has a recessed cross sectional shape as shown,for example, in FIG. 1 .

However, at the axial ends 61, 62 of the diffuser 10, the diffuser basesurface 34 is inclined to provide a gentle transition between therecessed surface shape and an end surface shape which correspondsgenerally to the somewhat bulging shape of the inflated but notstretched flexible member 20, as illustrated in FIG. 4 . As foreshadowedabove, this allows a gentle transition between the axially central andend shapes of the flexible member 20, assisting in reducing stress on,and premature damage to, the flexible member 20.

The first end and second end transitions in the illustrated embodimentare provided by shaped end pieces 1000, 1200, which are also illustratedseparately in FIGS. 10 and 12 , respectively.

Each of the shaped end pieces 1000, 1200 comprises a blocking portion1010, 1210 and a tapered region 1020, 1220.

The blocking region 1010, 1210 is shaped and dimensioned tosubstantially fill an axially short length of the recess provided by therecessed main surface 32, and further to provide a first support surfacepart 1012, 1212 extending beyond the recess, to support an end region ofthe flexible member 20 in its inflated but not stretched shape. Thus,the blocking region may have a transverse cross sectional shape which issubstantially the same as the cross sectional shape of the shape of theinternal compartment 50 as illustrated in FIG. 4 (as can be seen in FIG.12 ).

The tapered region 1020, 1220 is contiguous with the blocking region1010, 1210 and provides a base engaging surface 1022, 1222 which isshaped to conform closely to the recessed main surface 32 of thediffuser base body 30, and a second support surface part 1024, 1224which in use extends from the first support surface part 1012, 1212 tothe recessed main surface 32 of the diffuser base body 30. The taperedregion 1020, 1220 thus reduces in both height and lateral width as itextends away from the blocking region 1010, 1210.

The shaped end pieces 1000, 1200 may be attached to the diffuser basebody 30 in any desired manner. By way of non-limiting example, thiscould be achieved by use of a suitable glue or adhesive, sealant, doublesided tape, solvent welding material or fasteners (screws or clips). Itwould also be possible to hold them in place using certain types ofclamping member used to retain a flexible member (membrane) in sealedconnection with the rest of the diffuser at the diffuser ends. Ifnecessary, appropriate seals, such as O-rings or other seals, could beused to provide sealed integrity of the diffuser, including the interiorcompartment 50, as required. As foreshadowed elsewhere, the taperedshape provided by the shaped end pieces 1000, 1200 could, if desired, beprovided by appropriately shaped end regions of the diffuser base body30.

The shaped end piece 1000 used at the first end 61 of the diffuser 10provides an air inlet arrangement 1050, integrally formed therewith. Theair inlet arrangement 1050 comprises a passage 1030 which extendsthrough the shaped end piece 1000 and which has a gas outlet 1032provided as an opening in the second support surface part 1024 and a gasinlet 1034 provided by a pipe connection 1036 in fluid communicationwith the passage 1030 and projects externally of the diffuser 10. Thepipe connection 1036 is adapted for connection to an air supply pipe orhose, and may comprise any suitable type of connection, for example, amale, or spigot-type, connection, or a female, or socket-type,connection. Further, any desired type of connection-securingarrangement, such as a screw threaded or other type of hose or pipecoupling may be used.

The air inlet 1050 may be provided with a check valve 1060 (sometimescalled a non-return valve) as a precaution against any liquid whichmight have undesirably entered the interior compartment 50 flowing intothe gas supply pipe (not shown) that feeds gas to the diffuser. Manytypes of check valve are known per se, and any suitable check valvearrangement could be used (for example, a ball check valve, a diaphragmcheck valve, a swing check valve or the like). In the illustratedembodiment, the check valve 1060 is a lift check valve provided at theopening 1032 and comprises a disc or lift 1062, which can be lifted offa seat formed by the opening 1032, and which is retained in the openingby a stem 1064 attached to the a disc or lift 1062 being retained in aguide 1066 which is mounted in the opening. A seal 1068 may be providedbetween the disc 1032 and the opening 1032 to enhance sealing when thecheck valve 1060 is closed. The manner in which a lift check valve workswill be understood by the skilled addressee, and will not be describedin further detail.

In this embodiment, in order to accommodate the pipe part of the airinlet, and allow the shaped end piece 1000 which includes the pipe partto be fitted on to the diffuser body 30, in-use upper wall 34 of thediffuser body 30 is provided with a cut-out 1070 at the (or each) end ofthe diffuser 10 at which a shaped end piece with a pipe is to be fitted.FIG. 10(c) shows an end region of the diffuser body 30 in which acut-out 1070 is provided. The cut-out 1070 is formed by removing some ofthe in-use upper wall 34 between two remaining side regions 1072, 1074of the diffuser body 30. In this embodiment, the side regions 1072, 1074each comprise part of the structure that forms the attachment regions44, 46 and an adjoining side-part of the in-use upper wall 34. That is,some of the laterally central region of the in-use upper wall 34 ismissing, to provide the cut-out.

The shaped end piece 1000 may also incorporate a fail closed valvewhich, in the event of a membrane failure, will shut off air flow to thefailed diffuser thereby maintaining air pressure in the rest of the feedsystem to be maintained, and allowing the remaining diffusers in theaeration system to operate normally. It has been known for failure of adiffuser membrane (e.g. flexible member 20) to result in the very largeamount of air escaping through the inoperative diffuser compromising theaeration process performed by other, connected, diffusers to an extentwhere the grid with the failed diffuser must be isolated from theaeration process.

A fail closed valve suitable for such use may comprise a valve which iseffectively a gas fuse valve, which is a type of valve known per se,used to prevent flow of gas therethrough in response to an undesirablygreat flow of gas. A fail closed valve suitable for use such use maycomprise a valve member which remains in an open (effectivelyinoperative) position when the air flow is below a threshold level, thethreshold level being above normal operating air flow levels, and whichmoves into a closed (or air shut-off) position in response to the airflow exceeding the threshold level, and then remains in the closedposition, despite the air flow level dropping due to operation of thevalve. In an embodiment the valve may comprise a member having a taperedsurface, which is arranged to be moved into engagement with acomplementary tapered surface in response to air flow above thethreshold level, with the engaged position corresponding to a closedposition of the valve member. The taper may be a ‘self-holding’ class oftaper, such as for example a Morse taper, so that after activation(closure) the valve remains in the closed condition despite the air flowlevel dropping (to zero and/or to below the threshold level) due tooperation of the valve. In one alternative the valve may comprise agate-like valve member which is normally open and is arranged to bemoved into a closed position in response to air flow above the thresholdlevel and a latch arrangement to retain the gate-like valve member inthe closed position after activation despite the air flow level dropping(to zero and/or to below the threshold level) due to operation of thevalve. While the fail closed valve may be incorporated into the shapedend piece 1000, such a valve may be provided elsewhere in the air supplysystem of a diffuser.

The shaped end piece 1200 is for blanking off the second end 62 of thediffuser 10, and therefore does not include an air inlet or internalpassageway. However, if it is desired to connect two or more diffusers10 in series, so that one diffuser supplies gas to the next in series,then a diffuser which supplies gas can have a shaped end piece at itssecond end which provides a gas outlet (not shown). In this case, theshaped end piece at the second end of the diffuser, which provides theoutlet, could be similar or identical to the illustrated shaped endpiece 1000, but without the check valve (and, of course, acting as a gasoutlet rather than a gas inlet).

FIGS. 11(a) and 11(b) show a shaped end piece 1100 which is similar tothe shaped end piece 1000, but a variation thereof which is shapedslightly differently. That is, a blocking region 1110 of end piece 1100extends further in the axial direction than does the blocking region1010 of end piece 1000, and correspondingly a first support surface part1112 extends further in the axial (length) direction of the diffuserthan does first support surface part 1012 (but is, like first supportsurface part 1012, provided to support an end region of the flexiblemember 20 in its inflated but not stretched shape. Further, taperedregion 1120, is axially shorter than the tapered region 1020 of shapedend piece 1000, and the boundary between the first and second supportsurface parts 1124, 1112 is curved, rather than being substantiallystraight like the boundary between the first and second support surfaceparts 1024, 1012, so that the first and second support surface parts1124, 1112 overlap in the axial direction.

FIGS. 14(a) and 14(b) illustrate an embodiment of a retaining clamp1400, which is an embodiment of an end sealing part.

The retaining clamp 1400, in this embodiment, comprises an end clampingportion 1410 which is adapted to press or clamp an end region of theflexible member 20 against an end of the diffuser. Thus, a seal can beprovided between the flexible member 20 and an end of the diffuser bodyand/or tapered end piece.

The retaining clamp 1400, in this embodiment, comprises an axiallyextending upper clamping portion 1420 (which extends somewhat and, inthis embodiment, a short distance, in the axial direction of thediffuser). The axially extending upper clamping portion 1420 in useoverlies a region of the flexible member 20 close to the end thereof andis adapted to press or clamp this part of the flexible member 20 againsta surface of the diffuser body 30 and/or shaped end piece 1000, 1200which extends in an axial or length direction of the diffuser. In thisembodiment, the axially extending upper clamping portion 1420 in usepresses the corresponding part of the flexible member 20 against thefirst support surface part 1012, 1212 of a shaped end piece 1000, 1200.

In this embodiment, the retaining clamp 1400, further comprises anaxially extending lower clamping portion 1430 (which extends somewhatand, in this embodiment, a short distance, in the axial direction of thediffuser). The axially extending lower clamping portion 1430 in useunderlies a region of the flexible member 20 at to the end thereof andis adapted to press or clamp this part of the flexible member 20upwardly against a surface of the diffuser body 30 and/or shaped endpiece 1000, 1200 which extends in an axial or length direction of thediffuser. In this embodiment, the axially extending lower clampingportion 1430 is contoured to follow the curves of a bottom surface ofthe end part of the diffuser base, which in this embodiment, at theinlet end of the diffuser, is provided by the end regions of the sideregions 1072, 1074 of the diffuser body 30 on either side of the cut-out1070, and a bottom surface of an end part of the shaped end piece 1000which extends between the side regions 1072, 1074. The axially extendinglower clamping portion 1430 thus comprises first and second lateral sideparts 1433, 1436 contoured to fit the lower surfaces of the side regions1072, 1074 and a more laterally central part 1439, contoured to fit thelower surface of the shaped end piece 1000.

The retaining clamp 1400, further comprises an attachment arrangementfor attaching it relative to the rest of the diffuser 10. The fixingarrangement may comprises one or more apertures, each for receipt offastening member therethrough. In this embodiment, two such apertures1412, 1414 are provided, each for receipt of a fastener, e.g. a threadedfastener such as a screw 1413, 1415 therethrough.

It will be appreciated that an end sealing part which comprises only oneof an end clamping portion or an axially extending clamping portion may(in certain embodiments) be sufficient to provide a suitable end seal.In the illustrated embodiment, the retaining clamp 1400 comprises boththe end clamping portion 1410 and the upper and lower axially extendingclamping portions 1420, 1430, which is considered to assist in providinga robust seal and to assist assembly of the diffuser, includingretention of the end portion of the membrane during application of thefasteners and positioning of the retaining clamp 1400. The axiallyextending clamping portion 1420, especially where the surface whichbears against the external face 29B of the flexible member correspondssubstantially to the shape of the flexible member when the flexiblemember 20 is inflated by not stretched, can also assist in avoidingapplication of undue stresses to the flexible member.

FIG. 15(a) illustrates a length 1500 of flexible member 20 which hasbeen manufactured or tailored (for example, from a cross sectionallyuniform extrusion) for securing to a diffuser base body 30 of aparticular length, using shaped end pieces 1000, 1200 and retainingclamps 1400.

The length 1500 of flexible member 20 provides an end region 1510 in aform suitable for being passed around or over an end of the diffuserbase body 30 and an axially outer end of a shaped end piece 1000, 1200.In this embodiment, the end region 1510 is free from sealing strips 25,26 which extend along most of the length 1500 of flexible member 20. Ifthe length 1500 of flexible member 20 is prepared from a crosssectionally uniform extrusion, the end parts of the sealing strips 25,26 may be simply cut or trimmed off. The end region 1510 is alsoprovided with apertures 1512, 1514 for passage of fastening members(e.g. screws 1413, 1415) therethrough. The apertures 1512, 1514 may beformed in appropriate positions prior to attachment of the length 1500of flexible member 20 to the diffuser base body 30, or if appropriatetaking into consideration the characteristics of the flexible member 20may be made after attachment to the diffuser base body 30 andpositioning of a retaining clamp 1400, for example, by insert of screwsor a separate step such as use of a heated awl or the like. A further,opposed end region 1520 may correspond to the end region 1510.

FIG. 15(b) illustrates schematically the shape of a lateral half of thelength 1500 of flexible member 20 when it is secured to a diffuser basebody 30 using shaped end pieces 1000, 1200 and retaining clamps 1400,but does not show those other components of the diffuser 10.

With reference to FIG. 16 , the sealed attachment of the length 1500 offlexible member 20 to the diffuser base body 30 can be performed asfollows. It will be appreciated that FIG. 16 shows only one end, butthat the arrangement at the other end may correspond, and will beapparent to the skilled addressee from the following description. Inthis embodiment, the sealed attachment may be performed by inserting(and securing) the sealing strips (25, 26, but not shown in FIG. 16 ) ofthe flexible member 20 in the corresponding grooves 45, 47 of thediffuser base body 30, and then wrapping end regions 1510 (which isshort in axial length and which does not have sealing strips 25, 26)around the end of the diffuser body, including around the terminal(blocking region) end of the shaped end piece 1000, and then retainingthe end region 1510 of the flexible member 20 in sealed connection withthe other components by applying and securing retaining clamp 1400 overthe axial end of the diffuser base body 30 and shaped end piece 1000.The wrapping of the end regions 1510 around the end of the diffuser bodywill include some stretching of the end regions 1510. The assembly issecured by screws 1414, 1415 which are passed through the apertures1412, 1414 in the retaining clamp 1400, through the apertures 1512, 1514in the membrane, and into the grooves 45, 47 of the diffuser base body30. Clamping forces applied by the retaining clamp 1400 may beincreased, or adjusted, as needed by adjustment (tightening orloosening) of the screws, to provide a desired seal.

The diffuser 10 may include mounting plates 1700 for mounting thediffuser to a floor of a tank, or to a frame (not shown).

FIGS. 17 to 19 illustrate an embodiment of a two part mounting plate1700 for mounting the diffuser to a floor of a tank, or to a frame.

In this embodiment, the two part mounting plate 1700 comprises twosubstantially identical mounting plate parts 1700A, 1700B.

With reference to one mounting plate part 1700A, each of the parts1700A, 1700B comprises a groove 1710 for accommodating at least some ofa side region of the diffuser 10, such that the mounting plate part canslide along the engaged side region in the axial direction of thediffuser 10.

In the illustrated embodiment, the groove is for accommodating part ofone of the inwardly directed flange walls 40, 42.

Each mounting plate part 1700A, 1700B has a laterally inwardly directedpart 1702 which in use projects from the groove 1710, part of thedistance towards the side of the diffuser 10 which is not engaged by thegroove 1710, so that in use it extends substantially laterally inwardlyfrom the engaged side of the diffuser, but across a distance less thanthe entire width of the diffuser 10.

Each mounting plate part 1700A, 1700B further comprises a laterallyoutwardly directed part 1704 which in use projects from the groove 1710,laterally outwardly relative to the diffuser. The laterally outwardlydirected part 1704, provides a fixing formation 1706, in thisembodiment, in the form of a reinforced aperture, for facilitationfixing of the mounting plate 1700 to a mounting structure such as thefloor of a tank or a frame for mounting diffusers thereon.

The mounting plate part 1700A further comprises an engaging formationfor engaging the other mounting plate part 1700B. The engagingformation, in this embodiment, comprises a projection 1720 forengagement within a complimentary recess of the other mounting platepart 1700B, and a recess 1730 for receiving a complimentary projectionof the other mounting plate part 1700B.

In this embodiment, the groove 1710, the projection 1720 and the recess1730 extend in substantially parallel directions.

In use, the mounting plate part 1700A, with a first-side inwardlydirected flange wall 40 engaged within its groove 1710, can slide alongfirst-side inwardly directed flange wall 40 in the axial direction ofthe diffuser, and the other mounting plate part 1700B, with asecond-side inwardly directed flange wall 42 engaged within its groove1710, can slide along the second-side inwardly directed flange wall 42,also in the axial direction of the diffuser.

Thus, in use, the two the mounting plate parts 1700A, 1700B can be slidtowards (and away from) each other.

Because the laterally inwardly directed part 1702 does not extend theentire width of the diffuser, it can be placed substantially in thechannel 48 of the diffuser 10 at substantially any desired axialposition along the length of the diffuser 10. Thus, each mounting platepart 1700A, 1700B can be positioned in engagement with the diffuser atsubstantially any desired axial position along the length of thediffuser 10.

In use, the mounting plate parts 1700A, 1700B are positioned inengagement with opposite sides of the diffuser 10 at axial positions ofthe diffuser 10 close to a position where it is desired to locate amounting plate, with the projection 1720 of each mounting plate part1700A, 1700B extending towards the other mounting plate part.

When the mounting plate parts 1700A, 1700B are slid into engagement, theprojection 1720 of each mounting plate part is received in thecomplimentary recess 1730 of the other mounting plate part, with a fitsufficiently tight to prevent relative lateral movement of the twomounting plate parts 1700A, 1700B.

The two mounting plate parts 1700A, 1700B thus effectively provide asingle mounting plate which can be used to mount the diffuser by use ofthe fixing formation 1706.

The two part mounting plate 1700 provides a mounting plate which can bereadily attached to the diffuser base body 30 at the required axiallocation rather than having to be inserted at an end and slid along fromthe end to the desired position. This becomes increasingly beneficial asthe axial length of the diffuser increases.

FIG. 19 illustrates how the mounting plate parts 1700A, 1700B in aparticular embodiment can be engaged with the (e.g. diffuser body 30).Each groove includes a widened region 1712 for allowing the mountingplate parts 1700A to be fully engaged with an inwardly directed flangewall 40, 42 by partial insertion into the groove 1710 and then rotationof the mounting plate parts 1700A, 1700B to provide full insertion ofthe flange wall 40, 42 into the groove 1710.

It should also be noted that the laterally outwardly directed part 1704is, when the mounting plate 1700 is assembled and horizontal, verticallyoffset from, and higher than the laterally inwardly directed part 1702.Thus, when fasteners such as screws or bolts (not shown) are used in theapertures 1705 to force the outwardly directed parts 1704 downwardly,substantial opposed torques (or rotational forces) will be applied tothe connections between the grooves 1710 and the flange walls 40, 42 andbetween the projections 1720 and the recesses 1730. These forceseffectively lock the mounting plate parts 1700A, 1700B together, andprevent sliding relative to the diffuser body, once the fasters aretightened.

It will be appreciated that a variation could provide two projections onone of the component parts of a two part mounting plate, and twocomplementary receiving recesses on the other of the component parts.Further variation could provide different numbers of projections andcomplementary receiving recesses, including the possibility of a singleprojection on one of the component parts of a two part mounting plate,and a single complementary receiving recess on the other of thecomponent parts.

An arrangement in which both parts, e.g. 1700A, 1700B, of the two partmounting plate are identical can assist in reducing manufacturing cost,for example, by requiring only a single mould, rather than two differentmoulds, for manufacture by injection moulding. Further, the parts, e.g.1700A, 1700B, are each smaller than a similar single-piece mountingplate would be, allowing use of a smaller injection mould and moulding,and hence providing a reduction in cost. Further, having both parts,e.g. 1700A, 17008, of the two part mounting plate identical means thatany two parts can be used together to provide the assembled mountingplate, avoiding the possibility of wasted time resulting from a workerinadvertently selecting two parts that cannot be assembled together, orin ensuring that parts are provided in usable sets or pairs.

FIGS. 20(a) to 20(c) illustrate a variation 2000 in which gas is fedinto a diffuser at an axially central region thereof, rather than froman end. In this embodiment, the diffuser 2000 is provided with a gasinlet which is centrally located. In such an embodiment, both ends mayhave shaped end pieces for blanking off the ends, so that the both ofthe shaped end pieces may be similar or identical to the shaped endpiece 1200 of FIG. 12 . Alternatively, the shaped end pieces may allowthe passage of air for connection of further diffusers at either or bothends. The central gas inlet may include a check valve, and an example isillustrated in FIGS. 13(a) and 13(b).

As foreshadowed above, the diffuser disclosed herein is designed to formits own “pipe” by creating an elongate interior compartment along whichair may be distributed along the length of the diffuser, so that noconvention pipe or hose, and no conduit defined entirely or almostentirely by the diffuser base body is required.

The ability of the diffuser to distribute gas along the length of thediffuser via the internal compartment is enhanced by incorporating arecessed or concave curve, rather than the flat or typical upwards orconvex curve into the part of the body of the diffuser that forms partof the boundary of the interior compartment. The recessed part can, butdoes not necessarily, extend across the entire surface of the body thatforms part of the boundary of the interior compartment, but at least inpreferred embodiments, should be sufficient to increase the crosssectional size of the interior compartment or “pipe” compared to thebody providing a planar surface to bound the interior compartment (allother things being equal).

This conduit or “pipe” effect means that diffusers can be provided withsignificantly longer axial length than many (possibly any) previouslycommercially available fine bubble strip diffusers. Diffusers inaccordance with the present disclosure have been demonstrated tosuccessfully deliver air to the end of a diffuser at least 12 m long.Diffusers in accordance with the present disclosure avoid the occurrenceof excessively high local velocities in the distributed gas, which canotherwise cause drag on the membrane thus cause the membrane to flutterand act in an unstable manner.

Further, use of longer diffusers allows fewer hose or pipe connections,and fewer components to be used, which can provide efficiencies in costand efficiency of assembly and/or installation.

Of course, shorter lengths are also possible with the discloseddiffusers if desired or necessary to meet the dimensions of the reactorto be aerated. These can be of any shape including rectangular, squareand circular or combinations of these, e.g. oxidation ditches.

The cross sectional shape of the diffuser base body disclosed herein issimple, making easier to form, for example by extrusion or pultrusionthan diffuser bodies that are more complex in cross sectional shape (forexample, because the body itself defines an interior conduit).

Further, some known diffusers using bodies formed of plastic and whichinclude a pipe-like or hollow diffuser body, are in use sufficientlybuoyant that resultant uplift forces require substantial ballast or moreor larger restraints (compared to at least some embodiments describedherein) to hold the diffuser in place while in service.

Another beneficial feature of at least some embodiments is that theunderside of the diffuser is unrestricted other than at mountingsupports (mounting plates). It does not include any additional lateralsupports, webs, or internal conduit parts that would increase thelikelihood of it holding o trapping biological material which couldputrefy. It has been known for the profile of some commerciallyavailable diffusers to undesirable trap mixed liquor within conduitparts thereof.

Another beneficial feature of at least some embodiments is that thediffuser is that the action of inflating the flexible member 20 to aconvex profile (as shown in FIG. 4 ), promotes the removal of any debriswhich may settle on the membrane during non-operating time. It will benoted that the diffuser 10, as a whole, has a profile which slopesdownwardly (as shown) from the top of the inflated membrane, and is freefrom upwardly extending external protrusions which would be likely totrap debris and prevent the removal of debris from the membrane when theflexible member (membrane) is inflated. (The action of air bubbles beingemitted from the diffuser aids the transport of debris material from theupper surface of the membrane and diffuser, but in some known diffusersthis has proven insufficient to avoid debris being trapped.)

FIGS. 21 and 22 illustrate alternative embodiments 2100, 2200, in whichthe recessed surface which bounds the interior compartment is much morerecessed, and has a much greater curvature than that illustrated inFIGS. 1 to 16 and 20 . This can provide an interior compartment 2150,2250 (and thus a resulting pipe or conduit, effectively formed by theinterior compartment) which has a greater cross sectional size for agiven width of the diffuser. For example, a radius of curvature, in thetransverse direction may be of the order of half the width of thediffuser. While embodiments of this type may be useful under somecircumstances, it is often undesirable to have a diffuser which is toonarrow, as this may adversely affect bubble distribution, and a suitablywide diffuser with an internal compartment with cross sectional shape asshown in FIG. 21 or 22 may be more buoyant than is desirable. Selectingan appropriate cross sectional shape may therefore include balancingcapacity to distribute gas along the length of the diffuser, diffuserwidth, buoyancy and other factors.

The cross sectional shape of the embodiment of FIGS. 1 to 5 isconsidered suitable for a wide range of typical wastewater aerationapplications, providing sufficient cross sectional area in the interiorcompartment for the distribution of air for diffusers up to 12 m long,the greatest length likely to be readily handled and transported, whileavoiding unnecessary buoyancy and associated uplift.

Of course, the above features or functionalities described in relationto the embodiments are provided by way of example only. Modificationsand improvements may be incorporated without departing from the scope ofthe invention.

Some examples of envisaged variations and alternative embodiments andvariations which may be incorporated without departing from the scope ofthe present disclosure are described hereafter.

Different attachment/sealing of the membrane to the diffuser base at theends may be used. A number of different type of devices and arrangementsfor sealing the membrane and base at the ends of strip diffusers areknown per se, and in variations or alternative embodiments any suitableknown type could be used. For example, any one or more of screwedclamps, spring clips, sealant, glue etc. could be used without departingfrom the scope of the present disclosure.

Different attachment/sealing of the membrane to the base at the lateralsides. Engagement of a bulb (whether integrally formed with the membraneor provided as a separate, spline-like, sealing strip) has beendescribed in detail, but it should be appreciated that there are otherknown arrangements for sealing the membrane and base along the lateraledges of strip diffusers, and in variations or alternative embodimentsany suitable known type could be used. For example, in one alternativeform of edge seal, known per se in the field of diffusers, the membranemay be clamped to the base along or adjacent the lateral sides thereof.In such an arrangement lateral side regions of the membrane may befolded over, or otherwise conformed in shape to, lateral side regions ofthe base either prior to or at least partly as a result of the actionof, application of one or more clamp members.

An issue that sometimes arises in use of diffusers for aeratingwastewater is that when warm humid air enters the piping system whichfeeds the diffusers, water may condense on the walls of the pipes(including the downcomer) which convey pressurised air from blowers orcompressors to the diffusers. The condensate may pool in low lying areasof the pipes and may build up over time, causing problems, especially ifthe height of the accumulated water reaches the height of the diffusermembranes. These problems can include adverse effects on airdistribution through the piping system, including reduced air flow atthe diffusers, and fouling of the back (interior) sides of the diffusermembranes. This issue can be exacerbated in intermittent aerationapplications. Water could be purged manually using a suitable manualpurge valve system. This would rely on plant operators performing suchpurging on a regular basis.

With reference to FIGS. 23 to 31 , a valve arrangement which can allowautomatic purging of water from a piping system which feeds airdiffusers will be described. It will be appreciated that the disclosedvalve arrangement may have other uses, particularly in situations wherewater is to be purged from submerged air (or other gas) supply pipes.

With reference to FIGS. 23 to 31 , a valve arrangement generallydesignated by the reference numeral 2300, comprises a float valvearrangement and a duckbill valve arrangement, which act together toallow purging of water from a feed pipe of an air diffuser whileresisting entry of water, in which the diffuser and feed pipe aresubmerged, into the feed pipe.

As shown in the exploded views of FIGS. 23 and 24 , the valvearrangement 2300 comprises a float member 2310, which in the illustratedembodiment is generally cylindrical in external shape and which has atapered lower end region 2312. The tapered lower end region 2312 issubstantially conical in shape in the illustrated embodiment.

The float member 2310 is, in use, provided within a tubular float guide2320, which is provided with slots or apertures 2322 for allowingpassage of water that is to be purged therethrough. In the illustratedembodiment the slots 2322 comprise first and second higher axiallyextending slots 2322A, which in this embodiment are diametricallyopposed, and a lower axially extending slot 2322B. In the illustratedembodiment the slots 2322A, 2322B each have an angular extent of about45 degrees (in the transverse circumferential direction of the floatguide 2320) and the lower axially extending slot 2322B has an angularseparation from each higher axially extending slot 2322A of about 45degrees. The lower axially extending slot 2322B allows water accumulatedon the floor of the air feed pipe to flow to the purge outlet, as willbe described in due course.

The valve arrangement 2300 further comprises a duckbill valve 2330. Theduckbill valve 2330 comprises a first end region 2332, which provides aninlet end of the duckbill valve 2330 and may also, in use, be regardedas defining a valve arrangement outlet 2333 through which water can bepurged. The first end region 2332 also provides an outwardly extendingflange 2332A. The duckbill valve 2330 further comprises a second endregion 2334, which provides an outlet end of the duckbill valve 2330.The second, outlet, end region 2334 of the duckbill valve 2330 comprisesopposed elastomeric parts which are adapted to be forced apart by excesspressure from an upstream (duckbill valve inlet end) direction to allowfluid to flow through the duckbill valve, but which are biased togetherto a valve closed configuration to resist or prevent flow of fluidthrough the duckbill valve in the reverse direction. In the illustratedvalve arrangement 2300 the duckbill valve is constructed in one piecefrom an EPDM rubber or similar flexible elastomer material and has anoperational diameter of between 4 mm to 6 mm, although embodimentsinclude duckbill valves with operational diameters up to about 20 mm ormore. It will be appreciated that the structure and operation ofduckbill valves is known per se, and will not be described in detailherein.

The valve arrangement 2300 further comprises a duckbill retainer 2340for retaining the duckbill valve 2330 relative to a valve housing part2350 (and, in the illustrated embodiment, relative to a pipe or the likefrom which water is to be purged). The duckbill retainer 2340 provides afirst end region 2342, an intermediate region 2343 and a second endregion 2344.

The intermediate region 2343 has an exterior cylindrical wall providedwith a male helical thread, which facilitates connection to the valvehousing part 2350.

The first end region 2342, which is above the intermediate region 2343in use, is of slightly smaller external diameter than the intermediateregion 2343 and provides a flange accommodating recess 2347 (shown inFIG. 24 ) for accommodating the outwardly extending flange 2332A of theduckbill valve 2330. The depth of the flange accommodating recess 2347is slightly smaller than the thickness of the flange 2332A, so that whenthe flange 2322A is located in the flange accommodating recess 2347(with a lower surface of the flange 2332A engaging the bottom of therecess) the uppermost part of the flange 2332A can project upwardly asmall distance out of the recess, and an upper surface of the flange2332A is slightly higher than, and proud of, an upper surface of theduckbill retainer 2340. By way of example, in an embodiment thethickness of the flange is 2 mm and the depth of the flangeaccommodating recess 2347 is 1.75 mm. This allows the upper surface ofthe flange to be forced against a surface provided by the valve housingpart 2350 (as will be described hereafter) to effect a seal 2332A, whilehelping to prevent undesired deformation of the flange 2332A by havingmost of the thickness of the flange 2332A located in and supported bythe flange accommodating recess 2347.

The second end region 2344, which is lower than the intermediate region2343 in use, provides a hexagonal exterior configuration to facilitatefastening and unfastening of the duckbill retainer 2340 to the valvehousing part 2350 using a rotational fastening tool of the type used tooperate a hexagonal head of a bolt, or a hexagonal nut.

The duckbill retainer 2340 is provided with a passageway 2346 whichextends substantially axially therethrough. In use the passageway 2346accommodates part of the duckbill valve 2330 and allows water to flowtherethrough. The axial passageway 2346 is of sufficient diameter togive clearance to the duckbill valve 2330 so that its operation is notcompromised. The flange accommodating recess 2347 may be regarded as awidened upper termination of the passageway 2346.

It will be appreciated that in the illustrated embodiment the checkvalve arrangement 2300 is incorporated into a shaped end piece 2400,which is suitable for feeding air into a first end of a diffuser andwhich has many similarities in form and function to shaped end piece1000 described above, the description of which should be consideredincorporated into the description of shaped end piece 2400. Further, itwill be appreciated that the following description in relation to theshaped end piece 2400, other than that relating to the purge valvearrangement, may be of direct relevance to the shaped end piece 1000 andother shaped end pieces described above.

The shaped end piece 2400 provides an air inlet arrangement 2450,integrally formed therewith. The air inlet arrangement 2450 comprises apassage 2430 which extends through the shaped end piece 2400 and whichhas a gas outlet provided as an opening 2432 in a support surface part2424 and a gas inlet 2434 provided by a pipe connection 2436 in fluidcommunication with the passage 2430. The pipe connection 2436 is adaptedfor connection to an air supply pipe or hose, and may comprise anysuitable type of connection, for example, a male, or spigot-type,connection, or a female, or socket-type, connection. Further, anydesired type of connection-securing arrangement, such as a screwthreaded or other type of hose or pipe coupling may be used.

The air inlet 2450 is provided with a check valve 2460 (sometimes calleda non-return valve) comprising a disc or lift 2462, which can be liftedoff a seat formed by the opening 2432, and which is retained in theopening 2432 by a stem 2464 attached to the a disc or lift 2462 which isretained in a stem guide 2466 provided in the opening 2432. A stemretainer 2467, which is of greater diameter than the stem 2464, is inuse attached to the bottom of the stem 2464 so that the stem is retainedin a part of the stem guide 2466 which is of large enough diameter toaccommodate the stem 2464, but impassable by the stem retainer 2467,thus limiting upwards travel of the lift 2462.

A seal 2468 is provided between the lift 2462 and the opening 2432 toenhance sealing when the check valve 2460 is closed.

As illustrated in FIG. 24 , and also FIGS. 25 and 26 , the shaped endpiece 2400 provides a substantially horizontally extending groove 2470into which an edge of an upper wall of a diffuser base may be receivedin order to facilitate connection of the shaped end piece 2400 to thediffuser base. In the illustrated example, the groove 2470 may be shapedto receive an edge of an upper wall 34 of diffuser body 30 which definescut-out 1070, as illustrated in FIG. 10(c) described above.

The valve arrangement further comprises a valve housing part 2350, whichin this embodiment is provided as part of the air inlet arrangement 2450(or air feed pipe) which feeds air to the diffuser. The valve housingpart 2350 provides an upper circular recess 2352, for seating the bottomof the tubular float guide 2320, and a lower circular recess 2354 foraccommodating much of the duckbill retainer 2340. The lower circularrecess 2354 provides a female helical thread on its internal wall, sothat the duckbill retainer 2340 can be screwed into the lower circularrecess 2354. An upper part 2356 of the lower circular recess 2354 is ofreduced diameter and in use receives at least part of the first endregion 2342 of the duckbill retainer 2340, and an in use upper part ofthe duckbill valve, including the flange 2332A. A small shoulder 2358 isprovided between the upper circular recess 2352 and the upper part 2356of the lower circular recess 2354, against which the upper part of theduckbill valve 2330, and in particular the part corresponding to theupper surface of the outwardly extending flange 2332A of the duckbillvalve 2330, is pressed, in use, by the duckbill retainer 2340. Thethreaded engagement of the duckbill retainer 2340 and lower circularrecess 2354 provide firm, sealed engagement of the flange 2332A againstthe shoulder 2358 by tightening of the threaded connection when theduckbill retainer 2340 is screwed into the lower circular recess 2354.Undesired deformation of the flange 2332A (and consequent deformation ofthe valve arrangement outlet 2333, which might compromise sealing) issubstantially prevented by most of the thickness of the flange 2332Abeing located in and supported by the flange accommodating recess 2347.The axial length of the first end region 2342 of the duckbill retainer2340 and the axial length of the upper part 2356 of the lower circularrecess 2354 are dimensioned to provide a good seal between the flange2332A and the shoulder 2358, while avoiding the possibility of the firstend region 2342 bearing unduly hard against (and possibly damaging) theshoulder 2358 when the intermediate region 2343 of the duckbill retainer2340 is fully tightened into the (main, wider part of the) lowercircular recess 2354.

The upper circular recess 2352 and lower circular recess 2354 are influid communication to provide an outlet passage through which water maybe purged. However, it should be appreciated that the minimum diameterof this outlet passage, at the small shoulder 2358, is larger than thediameter of the valve arrangement outlet 2333 provided (in use) by theduckbill valve 2330, so the opening of the duckbill valve effectivelyprovides the valve arrangement outlet 2333. As will be describedhereafter, this provides, in use, a part which the tapered lower endregion 2312 of the float member 2310 can seal against, and which beingmade of elastomer, rubber or the like, assists in providing an effectiveseal.

The outlet is preferably provided substantially at the lowest point ofthe diffuser air feed passage, and effectively provides an outlet in thefloor, or lowest part, of the air feed passage.

FIG. 25 is a schematic side view of the embodiment of FIG. 23 ,assembled, and in a passive, non-air flow configuration, showing someinternal detail in broken lines, and FIG. 26 is a schematic end viewthereof, also showing some internal detail in broken lines.

FIGS. 27 and 28 are, respectively, schematic cross sectional viewscorresponding to the sections B-B and A-A in FIGS. 26 and 25respectively, illustrating the assembly and configuration of the variousparts when the air feed system and diffuser are a in a passive, non-airflow state.

In the passive, non-air flow configuration illustrated in FIGS. 25 to 28, the diffuser check valve 2460 is closed and the lift 2462 and stem2464 are in their lowest positions. In this configuration the bottom ofthe stem retainer 2467 rests gently upon the top of the float member2310 enhancing sealing of the tapered lower end region 2312 against thevalve arrangement outlet 2333 provided by the duckbill valve 2330, andfurther maintaining the seal even in the presence of water which mayneed to be purged from the air feed passage.

Even in the passive, non-air flow configuration, when the head pressureof water outside the air feed passage is greater than the air pressurewithin the air feed passage, the duckbill valve 2330 is effective inpreventing water from entering the air feed passage, as the resilient‘lips’ of the duckbill valve form a watertight seal which is not brokenby the external water pressure.

FIG. 29 is a schematic side view of the embodiment of FIG. 23 ,assembled, and in an active, air flow, configuration, showing someinternal detail in broken lines.

FIG. 30 is a schematic longitudinal cross sectional view correspondingto the view of FIG. 27 , but showing the active, air flow,configuration, and FIG. 31 is a schematic transverse cross sectionalview corresponding to the view of FIG. 28 , but showing the active, airflow, configuration.

As illustrated in FIGS. 29 to 31 , when air is supplied to the diffuser,the diffuser check valve 2460 is opened and the lift 2462 and stem 2464are in their raised positions. In this configuration the bottom of thestem retainer 2467 is raised to be clear of the top of the float member2310, allowing the float member to rise, due to its buoyancy, if thereis pooled water which needs to be purged. A raised position of the floatmember 2310 is illustrated in FIGS. 29 to 31 . In the raised positionthe tapered lower end region 2312 of the float member 2310, is no longersealed against (nor in contact with) the valve arrangement outlet 2333provided by the duckbill valve 2330. Thus the valve arrangement outlet2333 is effectively opened, providing a fluid passageway between thepooled water on the floor of the air inlet passage and the duckbillvalve 2330. In the air supply state the air feed passageway ispressurised (normally to a pressure sufficient to expel air through thediffuser membrane into the surrounding water which is being treated) toa pressure greater than the head pressure of the water outside thediffuser and the air supply passage, and the air pressure inside the airsupply passage forces the water to be purged through the duckbill valve2430 in a purging action.

As the water to be purged is expelled from the air feed passage thewater level in the air feed passage reduces, and the float member 2310,which is floating on the pooled water, descends accordingly. When allwater the water to be purged has been expelled from the air feed passagethe float member 2310 reseats the tapered lower end region 2312 thereofagainst the valve arrangement outlet 2333 provided by the duckbill valve2330, effectively sealing the outlet and preventing undesired expulsionof air through the purge valve arrangement 2300. The air pressure in theair feed passageway may assist in forcing the float member into sealedengagement with the valve arrangement outlet 2333.

The described embodiment can therefore provide a purge valve whichautomatically purges accumulated water from the air feed pipe when airpressure is applied, which controls undesired expulsion of pressurisedair therethrough, and which resists ingress of water, even when the airfeed passage is not pressurised.

The float member 2310 is an example of a purge control element which ismovable between a first control position in which it is not floating,for closing the water outlet when there is little or no accumulatedwater to be purged, and a second control position in which it floats dueto the presence of water to be purged, thereby leaving a water outlet(in this embodiment valve arrangement outlet 2333) open, so that watercan be purged therethrough.

The duckbill valve 2330 is an example of a flow check valve throughwhich water is, in use, purged, and is a one-way valve which allows flowof water therethrough in the purging direction and in use substantiallyprevents flow of water therethrough in the reverse direction.

FIGS. 32 to 36 illustrate an alternative embodiment of valvearrangement, generally designated by reference numeral 3200, in whichthe float member is in the form of a ball float 3210, rather than agenerally cylindrical member (designated 2310 in FIGS. 23 to 31 ) whichhas a tapered lower end region 2312. FIGS. 32 and 33 show exploded viewsand FIGS. 34 to 36 illustrate internal detail and configuration in thecircumstances that no air is being supplied to the diffuser, and nowater requiring purging has accumulated. Thus the ball float 3210 islocated on, and blocking the outlet. Initial consideration suggests thatthe use of a ball provides an inferior seal against the outlet, comparedto the generally cylindrical member (designated 2310 in FIGS. 23 to 35 )with its tapered lower end region 2312. It will also be appreciatedthat, as illustrated, in contrast to the embodiment of FIGS. 23 to 31 ,the position of the lift 2462 and stem 2462 of the diffuser check valve2460 do not provide a downward force upon the float member in the closedconfiguration of the diffuser check valve 2460 to retain the floatingmember against the outlet (although, the dimensions of the stem andrelated components could be adjusted to provide such a force, ifdesired).

It will be appreciated that further variations are possible.

In the described embodiments of the purge valve arrangement the purgevalve is provided in substantially the same location as the diffuser aircheck valve (e.g. 1060, 2460) and the tubular guide for the stem of thediffuser air check valve is extended to the floor of the air feedpassage and used as the tubular float guide 2320. However, it should beappreciated that the purge valve arrangement need not be provided at oradjacent the diffuser air check valve, and could be provided in anydesired position in the air feed passage.

Further, the floating member is not limited to the shapes described andcould be any appropriate desired shape. The floating member may behollow to provide a desired degree of buoyancy water, and/or may be orconstructed from a material which has a suitable specific gravity,currently considered to be provided by a density less than 80% of thatof water.

Further, if desired, a resilient member (e.g. a helical spring) or otherbiasing mechanism could be could be provided in the float guide (e.g.float guide 2320) to lightly bias the floating member downwardly andthereby improve sealing of the floating member against the outlet, whilenot preventing floating of the float member in the presence of water tobe purged (at least, not in an active, air flow, state of the valvearrangement).

Further, although an example of a suitable assembly has been provided,alternatives are possible. For example, in the described embodiments theduckbill retainer is described as connecting to the valve housing partby means of screw threaded connection, but alternatives such as gluingor press fitting are possible.

The invention claimed is:
 1. An elongate diffuser comprising: a diffuserbase comprising a diffuser body; a membrane attached to the diffuserbody; wherein the membrane is connected to the diffuser body so thatintroduction of gas at a working pressure into the diffuser displacespart of the membrane from contact with the diffuser body to provide anelongate sealed compartment between the membrane and a surface providedmainly or wholly by the diffuser body, the compartment having a firstlateral side interface region where the membrane contacts the diffuserbody, a laterally intermediate region where the membrane is spaced apartfrom the diffuser body and a second lateral side interface region wherethe membrane contacts the diffuser body, and wherein gas can pass fromthe compartment through the membrane for aeration of a fluid in whichthe diffuser is immersed; wherein the diffuser body surface which boundsthe compartment comprises a recessed portion which is recessed away fromthe membrane between the first lateral interface region and the secondlateral interface region, compared to a planar surface extending betweenthe first lateral side interface region and the second lateral sideinterface region, to thereby provide the compartment with a largertransverse cross sectional size than would be provided by a planarsurface extending from the first lateral side interface region to thesecond lateral interface region; wherein a gas inlet is provided at afirst axial end region of the diffuser body, and the compartmentdistributes gas between the inlet and a second axial end of the diffuserbody; and wherein a gas inlet pipe of the diffuser provides a purgevalve comprising: a purge control element movable between a firstcontrol position for closing a water outlet when there is little or noaccumulated water to be purged, and a second control position foropening the water outlet in response to the presence of water to bepurged; and a flow check valve through which water is, in use, purged,said flow check valve being a one-way valve which allows a flow of watertherethrough in a purging direction and in use substantially preventsflow of water therethrough in a reverse direction.
 2. The elongatediffuser according to claim 1, wherein the diffuser provides a gasoutlet at the second axial end region thereof, so that the compartmentcan be used for distributing gas from a gas supply to another diffuser.3. The elongate diffuser according to claim 1, wherein the diffuser hasa length of at least 6 metres, a width of between about 10 cm and about20 cm, or a length to width ratio of at least about
 20. 4. The elongatediffuser according to claim 1, wherein when substantially no gaspressure is provided to the diffuser, the membrane is in a relaxed orcollapsed state, so that the compartment does not exist; when a first,lower, level of gas pressure is provided to the diffuser, the membraneis inflated, but not stretched, to provide said compartment, which inthis state has a first, smaller, cross-sectional size; when a second,higher, level of gas pressure is provided to the diffuser, the membraneis inflated, and also stretched, to increase the spacing between themembrane and the diffuser body at the laterally intermediate region ofthe compartment, so that in this state the compartment has a second,greater, cross-sectional size.
 5. The elongate diffuser according toclaim 1, wherein at least one axial end region the membrane is sealedwith respect to a surface of the diffuser base such that a transverselyextending region of the membrane is retained in a substantially convexcross sectional shape irrespective of whether the membrane is inflated.6. The elongate diffuser according to claim 1, wherein at least oneaxial end region of the compartment is at least partially defined by abase surface end portion which is shaped to provide a smooth transitionfrom a transverse cross sectional shape that is substantially convexcloser to the corresponding end of the diffuser to a transverse crosssectional shape that is recessed closer to an axial centre of thediffuser.
 7. The elongate diffuser according to claim 6, wherein atleast one base surface end portion is provided by an end piece componentmanufactured separately to the diffuser body, and the diffuser basecomprises said diffuser body and said at least one end piece component.8. The elongate diffuser according to claim 7, wherein at least one saidend piece component provides a blocking region which at least partiallyblocks a recess provided by the recessed portion of the diffuser body,at an end region of the diffuser.
 9. The elongate diffuser according toclaim 1, wherein the flow check valve comprises a flexible part which isdeformable by positive net fluid pressure on an upstream side thereof,in a water purge flow direction, into an open configuration.
 10. Theelongate diffuser according to claim 9, wherein the flexible part of theflow check valve comprises an elastomer material, or wherein theflexible part of the flow check is configured to remain in asubstantially closed configuration in the circumstances of positive netfluid pressure on a downstream side thereof, in a water purge flowdirection.
 11. The elongate diffuser according to claim 1, wherein theflow check valve comprises a duck-bill valve.
 12. The elongate diffuseraccording to claim 1, wherein the purge control element comprises afloat, and the purge valve further comprises a float restraining memberpositionable in a first, float restraining, position to retain the floatsubstantially in the first, non-floating, position and moveable byproviding increased air pressure in a vessel from which water is to bepurged.
 13. The elongate diffuser according to claim 1, wherein the flowcheck valve is provided downstream, in a water purge flow direction, ofthe water outlet.
 14. The elongate diffuser according to claim 1,wherein the purge control element comprises a float, wherein the firstcontrol position corresponds to a non-floating position of the float,and wherein the second control position corresponds to a floatingposition of the float.
 15. The elongate diffuser according to claim 14,wherein the water outlet comprises a seat engageable by the float. 16.The elongate diffuser according to claim 1, wherein the water outletcomprises an inlet part of the flow check valve.
 17. An elongatediffuser comprising: a diffuser base comprising a diffuser body; amembrane attached to the diffuser body; wherein the membrane isconnected to the diffuser body so that introduction of gas at a workingpressure into the diffuser displaces part of the membrane from contactwith the diffuser body to provide an elongate sealed compartment betweenthe membrane and a surface provided mainly or wholly by the diffuserbody, the compartment having a first lateral side interface region wherethe membrane contacts the diffuser body, a laterally intermediate regionwhere the membrane is spaced apart from the diffuser body and a secondlateral side interface region where the membrane contacts the diffuserbody, and wherein gas can pass from the compartment through the membranefor aeration of a fluid in which the diffuser is immersed; wherein thediffuser body surface which bounds the compartment comprises a recessedportion which is recessed away from the membrane between the firstlateral interface region and the second lateral interface region,compared to a planar surface extending between the first lateral sideinterface region and the second lateral side interface region, tothereby provide the compartment with a larger transverse cross sectionalsize than would be provided by a planar surface extending from the firstlateral side interface region to the second lateral interface region;wherein a gas inlet is provided at a first axial end region of thediffuser body, and the compartment distributes gas between the inlet anda second axial end of the diffuser body, wherein the diffuser isprovided with a mounting plate for mounting the diffuser to a support,the mounting plate comprising two mounting plate parts which can beconnected to provide the mounting plate.
 18. The elongate diffuseraccording to claim 17, wherein each of the two mounting plate parts can,when separated from the other, be operatively engaged with the diffuserbody at substantially any desired axial position along the length of thediffuser body but when connected together can only be disengaged fromthe diffuser body at predefined axial positions.
 19. The elongatediffuser according to claim 17, wherein when the mounting plate partsare not connected, neither extends across the full distance betweenengaged side portions of the diffuser, but when they are connected thecombined two-part mounting plate extends between the engaged sideportions of the diffuser and can thereby be retained in a fixed positionrelative to the diffuser.
 20. The elongate diffuser according to claim17, wherein each mounting plate part provides a connection formation forconnecting with a connection formation of the other mounting plate part,and the two mounting plate parts are substantially identical.